For example, usually, oxygen inevitably contained in a polished wafer made by the Czochralski (CZ) process is partly precipitated to form a gettering site in the device fabrication process.
Here, when heat treatment is performed on a silicon wafer, oxygen contained in the wafer reacts with silicon to form oxygen precipitates (bulk micro defects, BMDs). It is known that if this oxygen precipitation excessively proceeds, the mechanical strength of the silicon wafer decreases, slip dislocations are formed even under low load stress in the device fabrication process, and the wafer is warped (for example, see NPL 1 (B. Leroy and C. Plougonven, Journal of the Electrochemical Society, 1980, Vol. 127, p. 961) and NPL 2 (Hirofumi Shimizu, Tetsuo Watanabe and Yoshiharu Kakui, Japanese Journal of Applied Physics, 1985, Vol. 24, p. 815)). Further, NPL 3 (Koji Sueoka, Masanori Akatsuka, Hisashi Katahama and Naoshi Adachi, Japanese Journal of Applied Physics, 1997, Vol. 36, p. 7095) describes that a larger size of BMDs increases the formation of slip dislocations caused when a thermal stress is applied to a wafer.
Since such a formation of slip dislocations caused in a device fabrication process reduces the yield of silicon devices, it is important to provide a silicon wafer in which slip dislocations are not formed even after heat treatment in the device fabrication process is performed. With respect to the control of such slip dislocations, WO 2006/003812 A (PTL 1) describes that a reduced size of BMDs increases the stress causing the formation of slip dislocations from the BMDs, which suppresses the reduction in the strength of the silicon wafer caused by oxygen precipitations.
Further, JP 2008-103673 A (PTL 2) describes that BMDs having a small size are densely formed in the wafer and the density of BMDs having a large size is minimized, thereby effectively suppressing the formation of slip dislocations.